Re: [PATCH 1/3] gpio: Add GPIO delay driver

Peng Fan
2026-01-30T07:21:28Z

Hi Michal,

On Thu, Jan 22, 2026 at 01:50:33PM +0100, Michal Simek wrote:
>Add a GPIO controller driver that provides configurable delays when
>setting GPIO output values. This is useful for hardware that requires
>specific timing delays during power sequencing or GPIO state changes.
>
>The driver wraps underlying GPIO controllers and adds programmable
>ramp-up and ramp-down delays specified in microseconds through the
>device tree. Each GPIO can have independent delay timings.
>
>Device tree binding matches Linux.
>
>Signed-off-by: Michal Simek <michal.simek@amd.com>
>---
>
> drivers/gpio/Kconfig | 8 +++
> drivers/gpio/Makefile | 1 +
> drivers/gpio/gpio-delay.c | 133 ++++++++++++++++++++++++++++++++++++++
> 3 files changed, 142 insertions(+)
> create mode 100644 drivers/gpio/gpio-delay.c
>
>diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
>index 60c5c54688e6..f69919abc05b 100644
>--- a/drivers/gpio/Kconfig
>+++ b/drivers/gpio/Kconfig
>@@ -1,3 +1,11 @@
>+config GPIO_DELAY
>+ bool "GPIO delay driver"
>+ depends on DM_GPIO
>+ help
>+ Enable the GPIO delay driver.
>+ This driver allows wrapping another GPIO controller and inserting
>+ ramp-up/ramp-down delays on output changes, as described in the
>+ Linux gpio-delay binding.

Add an entry for SPL?

> #
> # GPIO infrastructure and drivers
> #
>diff --git a/drivers/gpio/Makefile b/drivers/gpio/Makefile
>index 910478c0c7a9..fec258f59f52 100644
>--- a/drivers/gpio/Makefile
>+++ b/drivers/gpio/Makefile
>@@ -21,6 +21,7 @@ obj-$(CONFIG_ATMEL_PIO4) += atmel_pio4.o
> obj-$(CONFIG_BCM6345_GPIO) += bcm6345_gpio.o
> obj-$(CONFIG_CORTINA_GPIO) += cortina_gpio.o
> obj-$(CONFIG_FXL6408_GPIO) += gpio-fxl6408.o
>+obj-$(CONFIG_GPIO_DELAY) += gpio-delay.o
> obj-$(CONFIG_INTEL_GPIO) += intel_gpio.o
> obj-$(CONFIG_INTEL_ICH6_GPIO) += intel_ich6_gpio.o
> obj-$(CONFIG_INTEL_BROADWELL_GPIO) += intel_broadwell_gpio.o
>diff --git a/drivers/gpio/gpio-delay.c b/drivers/gpio/gpio-delay.c
>new file mode 100644
>index 000000000000..0c0d05ccb493
>--- /dev/null
>+++ b/drivers/gpio/gpio-delay.c
>@@ -0,0 +1,133 @@
>+// SPDX-License-Identifier: GPL-2.0
>+/*
>+ * Copyright (C) 2025 - 2026, Advanced Micro Devices, Inc.

Drop 2025?

>+ *
>+ * Michal Simek <michal.simek@amd.com>
>+ */
>+
>+#include <dm.h>
>+#include <dm/device_compat.h>
>+#include <dm/devres.h>
>+#include <asm/gpio.h>
>+#include <linux/delay.h>
>+
>+struct gpio_delay_desc {
>+ struct gpio_desc real_gpio;
>+ u32 ramp_up_us;
>+ u32 ramp_down_us;
>+};
>+
>+struct gpio_delay_priv {
>+ struct gpio_delay_desc *descs;
>+};
>+
>+static int gpio_delay_direction_input(struct udevice *dev, unsigned int offset)
>+{
>+ return -ENOSYS;
>+}
>+
>+static int gpio_delay_get_value(struct udevice *dev, unsigned int offset)
>+{
>+ return -ENOSYS;
>+}
>+
>+static int gpio_delay_set_value(struct udevice *dev, unsigned int offset,
>+ int value)
>+{
>+ struct gpio_delay_priv *priv = dev_get_priv(dev);
>+ struct gpio_delay_desc *desc = &priv->descs[offset];
>+ int ret = dm_gpio_set_value(&desc->real_gpio, value);
>+ u32 wait;

Check return value.
if (ret) {
dev_err(dev, "Failed to set gpio %d\n", offset);
}

>+
>+ dev_dbg(dev, "gpio %d set to %d\n", offset, value);
>+
>+ if (value)
>+ wait = desc->ramp_up_us;
>+ else
>+ wait = desc->ramp_down_us;
>+
>+ udelay(wait);
>+
>+ dev_dbg(dev, "waited for %d us\n", wait);
>+
>+ return ret;
>+}
>+
>+static int gpio_delay_direction_output(struct udevice *dev, unsigned int offset,
>+ int value)
>+{
>+ return gpio_delay_set_value(dev, offset, value);
>+}
>+
>+static int gpio_delay_xlate(struct udevice *dev, struct gpio_desc *desc,
>+ struct ofnode_phandle_args *args)
>+{
>+ struct gpio_delay_priv *priv = dev_get_priv(dev);
>+
>+ if (args->args_count < 3)
>+ return -EINVAL;
>+
>+ if (args->args[0] >= 32)
>+ return -EINVAL;
>+
>+ struct gpio_delay_desc *d = &priv->descs[args->args[0]];
>+
>+ d->ramp_up_us = args->args[1];
>+ d->ramp_down_us = args->args[2];
>+
>+ dev_dbg(dev, "pin: %d, ramp_up_us: %d, ramp_down_us: %d\n",
>+ args->args[0], d->ramp_up_us, d->ramp_down_us);
>+
>+ return 0;
>+}
>+
>+static const struct dm_gpio_ops gpio_delay_ops = {
>+ .direction_output = gpio_delay_direction_output,
>+ .direction_input = gpio_delay_direction_input,
>+ .get_value = gpio_delay_get_value,
>+ .set_value = gpio_delay_set_value,
>+ .xlate = gpio_delay_xlate,
>+};
>+
>+static int gpio_delay_probe(struct udevice *dev)
>+{
>+ struct gpio_delay_priv *priv = dev_get_priv(dev);
>+ struct gpio_delay_desc *d;
>+ ofnode node = dev_ofnode(dev);
>+ int i = 0, ret, ngpio;
>+
>+ ngpio = gpio_get_list_count(dev, "gpios");
>+ if (ngpio < 0)
>+ return ngpio;
>+
>+ dev_dbg(dev, "gpios: %d\n", ngpio);
>+
>+ priv->descs = devm_kmalloc_array(dev, ngpio, sizeof(*d), GFP_KERNEL);
>+ if (!priv->descs)
>+ return -ENOMEM;
>+
>+ /* Request all GPIOs described in the controller node */
>+ for (i = 0; i < ngpio; i++) {
>+ d = &priv->descs[i];
>+ ret = gpio_request_by_name_nodev(node, "gpios", i,
>+ &d->real_gpio, GPIOD_IS_OUT);

This will configure the GPIO as output and ACTIVE high/low flag will also
be used per my understanding.

Should the dir and value be deferred until set_value is invoked?

Regards,
Peng

>+ if (ret)
>+ return ret;
>+ }
>+
>+ return 0;
>+}
>+
>+static const struct udevice_id gpio_delay_ids[] = {
>+ { .compatible = "gpio-delay" },
>+ { }
>+};
>+
>+U_BOOT_DRIVER(gpio_delay) = {
>+ .name = "gpio-delay",
>+ .id = UCLASS_GPIO,
>+ .of_match = gpio_delay_ids,
>+ .ops = &gpio_delay_ops,
>+ .priv_auto = sizeof(struct gpio_delay_priv),
>+ .probe = gpio_delay_probe,
>+};
>--
>2.43.0
>